Key Takeaways:
- From 6 August 2026, developments with a red line boundary of 0.2 hectares or less are exempt from mandatory biodiversity net gain, unless onsite priority habitat is negatively affected.
- Temporary developments granted planning permission for five years or less are also now exempt.
- Minor developments no longer have to show that onsite habitat delivery was considered before buying registered off-site biodiversity units.
- The separate exemption for self build and custom build housing has been removed.
- The changes only apply to planning applications made on or after 6 August 2026. Earlier applications continue under the previous rules.
The rules for mandatory biodiversity net gain (BNG) in England changed on 6 August 2026. The Biodiversity Gain (Town and Country Planning) (Amendments and Transitional Provisions) (England) Regulations 2026, laid before Parliament on 14 July 2026, introduce two new exemptions, give minor developments more choice over how they deliver their 10% gain, and remove the separate exemption for self build and custom build housing.
This article sets out each change in turn: what it covers, the conditions attached to it, and what it means in practice for developers, landowners and local planning authorities (LPAs).
The Four BNG Changes at a Glance
| Change | What it means from 6 August 2026 |
|---|---|
| New 0.2 hectare exemption | Developments with a red line boundary of 0.2 hectares or less no longer need mandatory BNG, unless onsite priority habitat is negatively affected |
| New temporary development exemption | Fully temporary developments with permission for five years or less are exempt, provided the land is reinstated |
| Simpler hierarchy for minor developments | Minor developments can buy registered off-site biodiversity units without first showing that onsite delivery was considered |
| Self build exemption removed | Self build and custom build schemes now follow the same BNG rules as other developments |
Why the Rules Changed
Mandatory BNG has applied to major developments in England since 12 February 2024, and to small sites since 2 April 2024. In May 2025 the government consulted on how the system was working for minor, medium and brownfield development, and the consultation received more than 25,000 responses.
The government confirmed the resulting amendments on 14 July 2026, when statutory instrument SI 2026/790 was laid before Parliament. The first four changes took effect on 6 August 2026. Others, including new exemptions for conservation projects and public parks, have been announced but do not yet have an implementation date.
The New 0.2 Hectare Exemption
A development is now exempt from mandatory BNG where the area within its planning red line boundary is no more than 0.2 hectares. The measurement covers the whole application site rather than the built footprint, so access roads, gardens and landscaping all count towards the threshold.
The exemption does not apply where the development would negatively affect an onsite priority habitat. Priority habitats are those identified as being of principal importance for biodiversity in England, such as lowland meadow or lowland heathland. If your site contains one, the standard BNG requirement remains.
This is a much wider exemption than the existing de minimis rule, which only covers developments affecting less than 25 square metres of onsite habitat or 5 metres of linear habitat such as hedgerow. The government's impact assessment estimates that the change takes around half of residential planning permissions out of mandatory BNG, that around 12% fewer baseline biodiversity units will be compensated as a result, and that demand for off-site units will fall by roughly 10%.
The New Temporary Development Exemption
Temporary development is also exempt from mandatory BNG where the whole development is temporary, planning permission is granted for a period of five years or less, and the land is reinstated at the end of that period.
The same priority habitat condition applies: a temporary scheme that would negatively affect an onsite priority habitat cannot use the exemption. It also does not cover phased developments where individual phases are temporary but the overall scheme is permanent.
Before this change, a time-limited permission could carry a 30 year habitat obligation for a development that might only exist for two or three years. The exemption removes that mismatch.
A Simpler Route to Off-Site Units for Minor Developments
The biodiversity gain hierarchy sets out the order in which gains should be delivered: avoid and reduce harm first, then enhance or create habitat onsite, then use registered off-site gains, with statutory biodiversity credits as the last resort.
Until August 2026, applicants had to show that onsite delivery had been considered before turning to off-site units. For minor developments, that step has now gone. Onsite habitat creation and registered off-site biodiversity gains can be considered at the same stage, so a minor development can go straight to off-site units from the outset. Statutory credits remain the final option, and major developments continue to follow the full hierarchy.
What Counts as Minor Development?
Minor development covers:
- Residential schemes of one to nine dwellings on a site below one hectare, or sites below 0.5 hectares where the number of dwellings is unknown.
- Non-residential schemes creating less than 1,000 square metres of floorspace, or with a site area below one hectare.
In practice, the flexibility matters for minor developments above 0.2 hectares, because anything at or below that size is now likely to be exempt altogether.
Off-Site Units and the 30 Year Obligation
The hierarchy change also shifts who carries the long-term responsibility. Gains delivered onsite must be secured and managed by the developer for at least 30 years, through a planning condition, planning obligation or conservation covenant, with management plans and monitoring along the way.
When a developer buys registered off-site units instead, the landowner or habitat bank that created those units carries the long-term management obligation. The developer purchases the units and records the allocation in their biodiversity gain plan. For a scheme of a handful of homes, taking on a 30 year management commitment for a small patch of onsite habitat was often the hardest part of BNG compliance. From 6 August 2026, those schemes can price registered off-site units into the project from day one. Our guide to buying biodiversity units explains the process step by step, and landowners considering creating units to sell can read our guide to selling biodiversity units.
Buy or sell Biodiversity Units on the UK's largest BNG Marketplace
- A network of over 1,500 registered buyers
- Browse 50,000 BNG units nearing £1.5 billion in value
- Hands-on support, whatever your BNG needs
Self Build and Custom Build Exemption Removed
Since mandatory BNG began, self build and custom build housing has had its own exemption, covering schemes of up to nine dwellings on sites of 0.5 hectares or less. That exemption no longer applies to planning applications made on or after 6 August 2026.
Self build projects now follow the same rules as any other development. Many single plots will fall within the new 0.2 hectare exemption instead, so the practical effect depends on site size. Larger self build and custom build schemes that exceed the new threshold will need to deliver 10% BNG in the usual way.
When the Changes Apply: Transitional Arrangements
The changes are not retrospective. They apply to planning applications made on or after 6 August 2026.
- Applications submitted before 6 August 2026 continue under the previous BNG rules, even where the application is validated or decided after that date.
- Planning permissions that have already been granted are unaffected.
- Applications under section 73 to vary an existing permission generally continue under the rules that applied to the original application.
If you are unsure which regime applies to your project, the date the application was made is the deciding factor. Our guide to BNG in the planning process covers how the requirement fits into an application.
What Has Not Changed
The core framework of mandatory BNG is still in place:
- Development in England that is not exempt must still deliver a minimum 10% biodiversity net gain.
- Habitat created or enhanced for BNG must still be secured and maintained for at least 30 years.
- Baseline and post-development units are still calculated with the statutory biodiversity metric.
- The existing exemptions continue, including householder applications, the de minimis exemption and high speed rail projects. See our full guide to developments exempt from mandatory BNG.
- Major developments keep the full biodiversity gain hierarchy, with onsite delivery considered before off-site units.
Changes Still to Come
The government has announced further amendments that are not yet in force and do not have confirmed dates:
- An exemption for development carried out for conservation purposes.
- A targeted exemption for parks, playing fields and public gardens.
- Updates to the statutory biodiversity metric.
The May 2025 consultation also included proposals on how the spatial risk multiplier applies to off-site units, so further change in that area is possible. We will update this article as new dates are confirmed.
FAQs
Is biodiversity net gain being scrapped?
No. The 10% requirement remains in place for development in England that is not exempt, and delivered gains must still be maintained for at least 30 years. The August 2026 changes remove the smallest and shortest-lived developments from the system and give minor developments more choice over how they deliver their gain.
Does the 0.2 hectare exemption apply to my site?
It applies where the area within your planning red line boundary is no more than 0.2 hectares, the development would not negatively affect an onsite priority habitat, and the application is made on or after 6 August 2026. The measurement covers the whole application site rather than the built footprint.
Which rules apply if my application was submitted before 6 August 2026?
The previous rules. The changes only apply to planning applications made on or after 6 August 2026, so earlier applications keep the BNG requirements that applied when they were submitted, even if they are validated or decided later.
What is the biodiversity gain hierarchy?
It is the order in which biodiversity gains should be delivered: avoid and reduce harm first, then create or enhance habitat onsite, then use registered off-site gains, with statutory biodiversity credits as the last resort. From 6 August 2026, minor developments can consider onsite delivery and registered off-site units at the same stage. Major developments still follow the full hierarchy.
Do self build projects now need biodiversity net gain?
The dedicated self build and custom build exemption has been removed for applications made on or after 6 August 2026. A self build plot of 0.2 hectares or less is likely to qualify for the new small site exemption instead. Larger schemes need to deliver 10% BNG like any other development.
Where can I buy registered off-site biodiversity units?
Registered units are created and sold by landowners and habitat banks across England, and the long-term management obligation stays with the seller. The Gaia BNG marketplace lists units for sale across the country, searchable by local planning authority and habitat type.
More Information:
